2 out of 3 plants die?

We live in AZ. We had 3 tropical hibiscus planted on the south side of our house. We can't seem to figure out why the two outside plants (one 5 yrs old, the other only 2 yrs old) died, but the middle plant is still alive? We just replanted but are hoping to find an answer to avoid losing the new plants. There were not bugs on the plants but my husband noticed ants under them when he replanted. The remaining plant is looking a little yellow but also has new growth on it.